The Astronomia family of tourbillons are Jacob & Co's own unique take on creating an astronomical complication. Typically, they're not intended to be highly accurate representations of actual astronomical cycles (the most sophisticated example of a watch that does that is, right now, probably Vacheron Constantin's Celestia). Rather, they're a kind of kinetic sculpture for the wrist, being based around a four-armed carrier system that supports a variety of additional displays or representations of heavenly objects.

The Astronomia watches also feature very thick cases with high-domed crystals, which emphasizes the three-dimensionality of the carrier structure (as well as providing a real vault-of-the-heavens visual effect). Although we've said that in general, accurate celestial cycles aren't what Jacob & Co. is after in these watches, in the case of the Astronomia Sky, there is a very precise indication of sidereal time, as well as of the stars overhead.

The entire carrier system rotates around the dial once every 20 minutes. At the end of each arm there are, moving clockwise, the dial showing the time; a sort of stylized rocket-ship running seconds indicator, which rotates on its own axis once per minute; a double axis tourbillon (which with the addition of the central point of rotation for the carrier system, is actually a triple axis tourbillon) and a rotating globe cut from an orange sapphire.

ADVERTISEMENT

The dial showing the time is fixed to a differential system so that it's always right side up, no matter the position of the carrier on which it's mounted. Just behind it, you can see the central globe, which rotates inside a hemisphere of tinted sapphire (the globe is hand-engraved titanium and turns once every 24 hours).

The tourbillon rotates around its innermost axis once every 60 seconds, and around its outer axis once every five minutes (and of course, circles the inside of the watch three times an hour).

The original Astronomia had a spherically faceted diamond, where here, in the Sky, you see an orange sapphire. The idea for the diamond was that it was a stylized representation of the Moon; the orange sapphire dispenses with that resemblance, but you can, since its period of rotation isn't intended to simulate any particular heavenly body, pretend it is the orange planet or star of your choice (I'd go for Mars, myself...it seems to go with the rocket ship on the opposite carrier). The stone has 288 facets and the cut, which was developed specifically for the gems used in the Astronomia, is actually patented. Since the central carrier rotates once every 20 minutes, the watch looks different every time you look at it, and if it's on your wrist, you're probably going to be looking at it a lot.

Now, we did mention that the Astronomia watches, in general, are not about astronomically accurate celestial cycles? The Astronomia Sky does, however, incorporate a sidereal time complication. You can find it in the deeply colored blued titanium dial, with its constellations and stars in 18k gold. Once per sidereal day, an oval representing the horizon orbits the dial, and the stars and constellations that appear inside it, are those which are currently visible overhead.

The transparent flanks of the case let you see the month indications on the side of the dial – the dial actually rotates also, making one full rotation per sidereal year.

You might think, given its size and complexity, that the Astronomia Sky is a heavy watch. It's certainly no lightweight (in any sense of the word) but it is much more wearable than you might think, thanks partly to the fact that so much of the body of the watch is of pretty lightweight materials (titanium and sapphire, for instance).

This kind of maximalist watchmaking is the sort of thing people used to try a lot more often, say, ten or so years ago, but it takes a tremendous amount of sheer brio to make it work, and you have to have a certain kind of talent for taking things really over the top that a lot of people think they have, but don't. It helps if there are some points of real technical interest behind the watch as well, and getting all those relatively massive components all working together on the carrier system is much, much harder than you'd think from the visually spectacular final result. As a piece of sheer showmanship there is very little out there that even comes close to the Astronomia Sky, and I find this particular model – with its sidereal day, year, and star map indications – the most compelling version yet.